The invention concerns a shaft-hub joint for transmission of torques between two equiaxial machine parts.
It is known that in power trains, for example such for use in rolling mills where the torque generated by the motor is transmitted via shaft trains--in a rolling mill, e.g., the working roll is powered through a jointed shaft--disturbances on the machine end being driven due to which a transmission of torque from the power input to the power output may be interrupted at continued operation of the power source cause a deformation in the power train, due to torsion, and eventual torsional fracture. The torsional fracture shows in the extreme case a fracture pattern of 45.degree. to the axis of torsion, due to the tensile stresses occurring in twisting. In the case of the rolling mill, for example, torque transmission between the power source and working roll is interrupted in the case of working roll jamming. Subsequent to the fracture, i.e., in the example after separation of the working roll from the power source and with simultaneous continued operation of the power source, the fracture face on the side of the drive train that is still joined to the power source is twisted relative to the now stationary fracture face located on the side of the working roll. Due to the superimposition of the fracture faces and due to the differences in inertia and speed of rotation between the parts of the power train that have been created by the fracture--the one connected to the power source and that joined to the working roll--the part joined to the power source undergoes an axial shift in its own direction. The continued drive motion imparted by the motor and the obliquely fashioned fracture lead generally to the occurrence of high axial forces which bring about a positional shift of individual elements of the power train, in the extreme case a heaving of the components out of their anchoring.
A known solution for avoidance of such incidents consists in fashioning the joint between power source and element being driven, not integrally in the form of a shaft train, but in at least in two parts, and to join these two parts in such a way that the torque transmission will be realized while also appropriate overload relief mechanisms are allowed to become effective which at high axial forces interrupt the transmission of torque. In the prior solutions, an element is used as a safety clutch which also functions as the rotationally fixed joint between the two parts, for example the two parts of the shaft train. The safety clutch serves the transmission of high torques and is provided with a system for torque limitation, such as is known for instance from DE 29 23 902.
This clutch comprises at least one thin-walled sleeve forming an axially extending wall of an essentially annular chamber which can be acted upon by a pressure medium so as to deform the sleeve essentially elastically in the radial direction and cause it to bind with a surface of an element on which the clutch is mounted. There are two options available for that purpose. In one option, the clutch becomes effective between the two machine parts to be joined, in that the clutch is designed as a bushing that consists of two sleeves welded to each other and whose cavity can be acted upon by a pressure medium, deforming the sleeves radially and locking the two machine parts onto each other. In the second option, the clutch embraces both machine parts and causes frictional engagement between both by deformation of only one sleeve. Bordering on the annular chamber is a duct arrangement with which a safety or clutch relief mechanism is coordinated. The relative motion between the surfaces of the two machine parts which are to be joined by frictional engagement or a specific torsional deformation of same can be caused to enter a state in which the pressure medium contained in the annular chamber can escape from it through the duct arrangement, thereby relieving the annular chamber. Hence, the clutch is adjusted to the desired torque of release. If this torque is exceeded due to an overload, slippage of the clutch occurs. The transmitted torque diminishes, since the effective coefficient of adhesive friction transforms to a coefficient of sliding friction. A relative motion between the shaft and hub takes place in the peripheral direction. Mounted for instance on the shaft, a shear ring shears off a shear valve which communicates with the duct arrangement or the annular chamber of the clutch.
With the shear valve(s) sheared off, the highly pressurized oil can expand freely, and the transmittable torque drops within a few milliseconds to zero.
To safeguard against axial force overloads, the clutch is adjusted to an appropriate admissible axial force to be transmitted, i.e., the internal pressure of the annular chamber is so set that with it the frictional engagement can be maintained only up to the level of the critical axial force. As the admissible axial force is exceeded, for example due to a fracture, the frictional engagement is eliminated and supplanted by a relative motion in the axial direction between the clutch and the elements joined to it. The disadvantage of this embodiment is that the clutch must be set to an appropriate axial force and designed accordingly. A simultaneous transmission of high torques with the same clutch can be realized only in rarest cases, since the surface pressures between clutch, shaft and hub that are required from transmission of the desired torque and the still admissible axial force may vary from one another depending on conditions of application. Owing to the equality of the forces that are required for elimination of the frictional engagement in the peripheral direction and in the axial direction, and owing to the desire to actuate the clutch relief mechanism at axial forces that are already relatively low as compared to the peripheral force, only low torques can be transmitted with clutches of such design.
Another option is relieving in the case of such a clutch the system for torque limitation, i.e., for release of the frictional engagement, at a selected axial force, by measuring the magnitude of the axial forces and transforming the measured value to a signal for release of the safety mechanism for torque limitation. But this option is characterized by a very high metrological and control expense, since the response times must be very short.
Therefore, the problem underlying the invention is to so advance a shaft-hub joint of the general type just described such that the aforementioned disadvantages will be eliminated. The shaft-hub joint should be suited for transmission of high torques, for instance for use with jointed shafts or universal shafts, and the overload relief mechanism is to be able to react to already low axial forces.
The structural conversion should be such that the overload relief mechanism will respond at a specific magnitude of the effective axial force. In doing so, the emphasis is on a low-cost realization of structure and function, with a small number of components of simple design. The entire arrangement is meant to excel by having a low manufacturing and assembly expense as well as simple and quick resetting after a response event.